Cooling system for therapeutic catheter

ABSTRACT

A heat exchanger to remove heat from coolant in a closed circuit cooling catheter includes two heat exchange stages. Each stage includes a heat exchange element, such as a group of hollow fibers, and a TEC array juxtaposed with the heat exchange element to remove heat from the element. The elements are in fluid series with each other and are separated from each other by a thermal barrier. A thermal interface can be provided between each element and its TEC array. In one embodiment, the thermal interface is a gel layer. In another embodiment, the thermal interface is an ethylene glycol bath.

FIELD OF THE INVENTION

The present invention relates generally to methods and apparatus forheating and cooling patients for therapeutic purposes, and moreparticularly to systems for treating brain trauma and brain ischemia byinducing hypothermia in a patient.

BACKGROUND

It has been discovered that the medical outcome for a patient sufferingfrom severe brain trauma or from ischemia caused by stroke or heartattack is degraded if the patient's body temperature rises above normal(38° C.). It is further believed that the medical outcome for many suchpatients might be significantly improved if the patients were to becooled relatively quickly to around 32° C. for a short period, e.g.,24-72 hours.

The affected organ, in any case, is the brain. Accordingly, systems andmethods have been disclosed that propose cooling blood flowing to thebrain through the carotid artery. An example of such systems and methodsis disclosed in co-pending U.S. pat. app. Ser. No. 09/063,984, filedApr. 21, 1998, owned by the present assignee and incorporated herein byreference. In the referenced application, various catheters aredisclosed which can be advanced into a patient's carotid artery andthrough which coolant can be pumped in a closed circuit, to remove heatfrom the blood in the carotid artery and thereby cool the brain. Thereferenced devices have the advantage over other methods of cooling(e.g., wrapping patients in cold blankets) of being controllable,relatively easy to use, and of being capable of rapidly cooling andmaintaining blood temperature at a desired set point.

As recognized in co-pending U.S. pat. app. Ser. No. 09/133,813, filedAug. 13, 1998, owned by the present assignee and incorporated herein byreference, the above-mentioned advantages in treating braintrauma/ischemic patients by cooling can also be realized by cooling thepatient's entire body, i.e., by inducing systemic hypothermia. Theadvantage of systemic hypothermia is that, as recognized by the presentassignee, to induce systemic hypothermia a cooling catheter or othercooling device need not be advanced into the blood supply of the brain,but rather can be easily and quickly placed into the relatively largevena cava of the central venous system. Moreover, since many patientsalready are intubated with central venous catheters for other clinicallyapproved purposes anyway, providing a central venous catheter that canalso cool the blood requires no additional surgical procedures for thosepatients.

Regardless of where the cooling occurs, however, it is clear that heatmust be removed from the coolant that flows through the catheter. Asrecognized herein, it is desirable that a cooling system for a coolingcatheter consume minimal energy and space. Small size is desired becausespace is often at a premium in critical care units. Moreover, as alsorecognized herein, for patient comfort it is desirable that such acooling system generate a minimum amount of noise. As still furtherunderstood by the present invention, it is desirable that the coolingsystem be easy to use by health care personnel, and that the portion ofthe cooling system that directly contacts the catheter coolant bedisposable. We understand that if the portion of the cooling system thatdirectly contacts the catheter coolant were not disposable, the portionundesirably would require sterilization by, e.g., autoclaving prior toreuse, because even though the coolant does not directly contact thepatient but is instead contained within the catheter, the potentialarises that through in-leakage or other means body fluid might indeedcontaminate the coolant. Accordingly, it is the object of the presentinvention to address one or more of the above-noted considerations.

SUMMARY OF THE INVENTION

A heat exchange system for a catheter includes at least one heatexchange element that is connectable to the catheter for receivingcoolant from the catheter, and at least one thermal electric cooler(TEC) in thermal contact with the heat exchange element for heating orcooling the element such that coolant is returned to catheter to heat orcool the catheter.

In a preferred embodiment, the heat exchange element is plastic. Morepreferably, the heat exchange element includes plural hollow fibers, or,the heat exchange element can include at least one non-linear plastictube. As another alternative, the heat exchange element can include abag that has plural fluid paths through the bag which are establishedby, e.g., heat-staking portions of the bag together. A thermal interfacesuch as an aluminum oxide gel or metallized plastic foil bag can besandwiched between the heat exchange element and the TEC to removablycouple the element to the TEC. Less desirably, the heat exchange elementincludes at least one metal tube in thermal contact with the TEC. Forcooling efficiency, two cooling stages can be used, with each coolingstage including a respective heat exchange element with associated TECassembly, and at least one thermal barrier is disposed between theelements.

In another embodiment, a heat exchange fluid is disposed between the TECand the heat exchange element such that the heat exchange element isdisposed in the fluid. The fluid can be cold ethylene glycol. Anagitator is disposed in the fluid to move the fluid.

In another aspect, a cooling system for a therapeutic medical deviceincludes at least one heat exchanger made at least partially of plastic.The heat exchanger receives coolant from the medical device and returnscoolant thereto. A thermal electric cooler (TEC) is in thermal contactwith the heat exchanger for removing heat from the heat exchanger.

In still another aspect, a cooling system includes catheter means forconveying coolant into a patient's body without directly contacting thecoolant with the body. Also, the system includes heat exchanger meanscommunicating with the catheter means for receiving coolant therefromand returning coolant thereto. Cooling means is in thermal contact withthe heat exchanger means for conveying heat away from the heat exchangermeans.

In yet another aspect, a controller is disclosed for establishing acontrol signal for controlling coolant temperature in a therapeuticcatheter cooling system. The cooling system can include a coolant pumpand at least one TEC, and the controller includes logic means thatreceive a desired patient temperature and a measured patienttemperature. The controller logic determines a control signal inresponse to the temperatures, with the control signal being sent to thecooling system for establishing the coolant temperature. Preferably, thecontrol signal is also established in accordance with a measured patienttemperature time derivative and/or time integral. As intended by thepresent invention, the control signal is used to establish at least oneof: a speed of the coolant pump, and an energization of the TEC.

The details of the present invention, both as to its structure andoperation, can best be understood in reference to the accompanyingdrawings, in which like reference numerals refer to like parts, and inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the cooling system in its intendedenvironment;

FIG. 2 is an exploded perspective view of one of two cooling stages ofthe present system;

FIG. 3 is a schematic top view of the cooling system, showing bothcooling stages;

FIG. 4 is a side view of an alternate cooling element;

FIG. 5 is a side view of another alternate cooling element;

FIG. 6 is a side view of yet another alternate cooling element, withportions of the aluminum casting cut away for clarity;

FIG. 7 is an exploded perspective view of one cooling stage of analternate embodiment of the present system, which uses an ethyleneglycol bath;

FIG. 8 is a side view of an alternate cooling element for the systemshown in FIG. 7;

FIG. 9 is a perspective view of another alternate cooling element forthe system shown in FIG. 7;

FIG. 10 is a schematic side view of the cooling system shown in FIG. 7;and

FIG. 11 is a flow chart of the control logic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1, a cooling system, generally designated10, for a therapeutic catheter 12 is shown. In the preferred embodiment,the catheter 12 is a cooling catheter that can be advanced into apatient's carotid artery or, more preferably, vena cava, to cool thepatient (and, when it is desired to warm the patient back up, to heatthe patient) to thereby improve the medical outcome for the patient whenthe patient has suffered from severe brain trauma or ischemia. Preferredcatheters are disclosed in the above-referenced patent applications.Less preferred catheters are disclosed in U.S. Pat. Nos. 5,411,477 and5,342,301 to Saab and U.S. Pat. No. 5,837,003 owned by Radiant Medical.While referred to herein as a "cooling system", it is to be understoodthat the system 10 more generally is a heat exchange system thatpreferably removes heat from the catheter 12 but that can also add heatthereto if necessary to correct "overshoot" of patient temperature andwarm the patient after cooling therapy.

As shown, the system 10 receives coolant from the catheter 12 via acoolant return line 14, and the system 10 supplies coolant to thecatheter 12 via a coolant supply line 16. Thus, the catheter 12 is aclosed circuit cooling system through which coolant is circulated toremove heat from the patient, with the coolant being cooled or heated bythe system 10 as more fully disclosed below. As set forth in theabove-referenced patent applications, the coolant preferably is abiocompatible liquid, such as saline. If desired, however,non-biocompatible fluids can be used to achieve lower coolanttemperatures than is otherwise available with saline.

The coolants lines 14, 16 can be IV lines or tubes or other suitablefluid conduits, such as metal (steel) tubes. When the coolant lines 14,16 are plastic tubes, they can be connected to the catheter 12 and thesystem 10 by suitable connecting structure, such as Luer fittings,interference fits, solvent bonding, heat staking, ultrasonic welding,and the like.

FIG. 1 shows that the cooling system 10 includes a heat exchanger 18(disclosed further below), a pump 20, and, if desired, a controller 22.Preferably, the pump 20 is a peristaltic pump, but other types ofpositive displacement pumps, such as but not limited to piston pumps androller pumps, or even centrifugal pumps, can be used. A peristaltic pumpis preferred in the present implementation because it can pump coolantwithout directly contacting the coolant, but instead simply by squeezinga tube through which the coolant flows. In this way, the pump 20 isreusable, and only the catheter 12 and portions of the system 10 comingin direct contact with the coolant need be made disposable to render anadvantageously disposable system.

As shown, the pump 20 takes a suction on the coolant return line 14 anddischarges coolant to the heat exchanger 18, from whence the coolantpasses back to the catheter 12 via the coolant supply line 16. It is tobe understood, however, that the pump 20 could be disposed on thedischarge side of the heat exchanger 18, if desired.

As further shown, the pump 20 includes an electric or other type ofmotor 24, and the controller 22 can be electrically connected to themotor 24 to control the rate at which coolant is pumped by the pump 20.Also, the controller 22 can be electrically connected to elements in theheat exchanger 18 to control the rate at which heat is added orsubtracted from the coolant. As more fully set forth below, thecontroller 22 can be implemented by a software-executing processor or bydiscrete logic circuits or other electronic circuitry device toestablish a desired patient temperature by appropriately controlling thepump 20 and/or heat exchanger 18.

As intended by the present invention, the desired patient temperature T₀can be input by means of a rheostat or keyboard or other input device26, or it can be preprogrammed into the controller 22. In any case, thecontroller 22 receives a temperature signal T_(P) from one or moretemperature sensors 28, with the temperature signals having beendigitized by means of an analog to digital converter 30 and processed ifdesired by a differentiator 32 and integrator 33, such that thecontroller can, if desired, receive a temperature signal, a signalrepresenting the time rate of change of patient temperature and a signalrepresenting the time integral of temperature, for purposes to beshortly disclosed. It is to be understood that the temperature sensor 28can be a thermistor, thermocouple, RTD, or other temperature sensingelement that can be orally or rectally placed in the patient or that canbe mounted on the catheter 12 or otherwise associated with the patient(e.g., the sensor 28 can be an infrared device) to detect a temperatureof the patient.

If desired, a heater "H" can be provided to heat coolant that has becometoo cold. When a heater is provided, heater inlet and outlet valvesH_(in), H_(out) can be opened to permit coolant to flow through theheater. Under these conditions, coolant inlet and outlet valves C_(in),C_(out) can be provided at the inlet and outlet of the cooling system 18and can be shut, to prevent coolant from entering the cooling system 18.It will readily be appreciated that under normal conditions, it isdesired to remove heat from the coolant, in which case the heater inletand outlet valves H_(in), H_(out) are shut and the coolant inlet andoutlet valves C_(in), C_(out) are open. The valves can be manuallycontrolled or, more preferably, are solenoid controlled, with the valvesolenoids being electrically connected to the controller 22 for controlthereby. Likewise, the heater "H" is controlled by the controller 22.Alternatively, no heater (and, hence, no heater inlet and outlet valves)need be provided. Instead, the TEC elements of the present invention canbe reversed to become warm instead of cool by reversing current flowthrough them, when it is desired to heat the coolant.

FIGS. 2 and 3 show the details of one preferred heat exchanger 18. Asshown, a first thermoelectric cooler (TEC) assembly 34 includes at leastone heat sink 36 from which heat can be removed by an array of fans 35.Also, the first TEC assembly 34 includes at least one cold plate 37 inthermal contact with the heat sink 36, and plural TEC elements 38 aresandwiched between the cold plate 37 and heat sink 36 in accordance withTEC principles known in the art. As known in the TEC art, the TECelements 38 are connected to source of electricity to cause thetemperature of the elements to change, and more particularly to cool thecold plate 37, with heat being removed from the TEC elements 38 by theheat sink 36. The TEC assembly 34 can be purchased from TE Technology ofTraverse City, Mich.

A first heat exchange element 40 is positioned against the cold plate 37as shown. Preferably, the heat exchange element 40 is disposable. In oneembodiment, the heat exchange element 40 is made of plastic, and morepreferably is made of plural co-parallel thin-walled hollow fibers 42that have inlet ends communicating with a coolant return line fitting 44that in turn is connected to the coolant return line 14. Also, thefibers 42 have outlet ends communicating with a coolant supply fitting46 that in turn is connected to the coolant supply line 16. The fibers42 can be held in a disposable plastic bag or other container 48 forconvenience, with the fibers 42 thus defining plural fluid paths throughthe bag. It is to be understood that the catheter 12, coolant lines 14,16, and heat exchange element 40 can be provided as an integrateddisposable product, with one of the lines 14, 16 being engaged with thepump 20 and with the bag or container 48 being disposed next to the coldplate 37 when it is desired to use the catheter 12 to cool a patient.

If desired, a layer or sheet 50 of aluminum oxide gel or mylar ormetallized plastic foil or other thermal interface material can besandwiched between the bag or container 48 and the cold plate 37. Forexample, a layer of gel made by Raychem can be provided with paperprotective layers on each face of the layer, and then the paper peeledaway and the gel applied to the bag or container 48 when it is desiredto engage the bag or container 48 with the cold plate 37. Then, the bagor container 48 with layer or sheet 50 is pressed, thermal interfacefirst, against the cold plate 37 to hold the bag or container 48 againstthe cold plate 37.

Although a single heat exchange element 40 with TEC assembly 34 can beused, more preferably at least two heat exchange elements withrespective TEC assemblies are used to establish a dual-element assembly41, as shown in FIG. 3, to effect comparatively efficient stagedcooling. As shown, the first heat exchange element 40 is in fluid serieswith a second heat exchange element 52, which in turn is closelyjuxtaposed with a second TEC assembly 54, such that coolant first passesthrough the first element 40 to be cooled therein, and then passesthrough the second heat exchange element 52 for further cooling. It isto be understood that the heat exchange elements 40, 52 can be identicalto each other in structure and operation, and that the heat exchangeassemblies 34, 54 likewise can be identical to each other in structureand operation. A thermal barrier 56 can be disposed between the heatexchange elements 40, 52 as shown, if desired. The thermal barrier 56can be a relatively thick block of thermal insulating foam or otherinsulative material. Additionally, more than one dual element assembly41 can be used. Indeed, as shown in FIG. 3 two or more dual elementassemblies 41 can be used in series. Or, if desired the coolant returnand supply lines 14,16 can be established by two lines each with eachset of lines being cooled in parallel with the other set by engagingeach set in respective dual element assemblies 14 that are arranged inparallel with each other.

FIG. 4 shows an alternative heat exchange element, generally designated60, which includes a plastic frame 62 that supports plural bundles 64 ofhollow fibers 66. Each bundle 64 can include an inlet fitting 68 and anoutlet fitting 70 for communicating cold fluid to the catheter 12 (FIG.1). If desired, the frame can be made of metal or ceramic or othermaterial, but is preferably plastic to promote disposability.

FIG. 5 shows yet another alternative heat exchange element, generallydesignated 72, which includes a foil or plastic bag 74 that has beenheat-staked along multiple locations to create a long fluid path 76 witha length that is greater than the dimension of the element 72 itself.The fluid path 76 communicates with an inlet fitting 78 and an outletfitting 80 for communicating cold fluid to the catheter 12 (FIG. 1).

A still further embodiment of the present heat exchange element is shownin FIG. 6, which shows a heat exchange element 82 having plural copperor steel fluid segments 84 embedded in a metal (e.g., aluminum) casting86. It is to be understood that the fluid segments 84 can be establishedby a single steel tube that is configured as shown and that communicateswith the return and supply lines 14, 16 shown in FIG. 1.

FIGS. 7-10 show an alternate cooling system, generally designated 100,which includes at least one heat exchange element 102 that has an inlet104 for receiving coolant from the coolant return line 14 (FIG. 1) andan outlet 106 for communicating coolant to the coolant supply line 16,or to a second stage heat exchange element as more fully disclosedbelow. In the embodiment shown in FIG. 7, the heat exchange element 102is configured as a coiled metal or plastic (e.g., PVC) tube. Inaccordance with the present invention, however, a heat exchange element108 shown in FIG. 8 can replace the element 102 shown in FIG. 7. Asshown, the heat exchange element 108 shown in FIG. 8 is a non-linearmetal or plastic tube, and more particularly is configured as acontinuous series of flattened "S"-shaped segments 110. FIG. 9 showsthat as yet another alternative, a heat exchange element 112 can includea bundle of hollow fibers 114 that are held in a bag or other container116 and that communicate with a fluid inlet port and outlet port118,120.

Regardless of which element is used and taking the element 102 shown inFIGS. 7 and 10 as an example, the element 102 is immersed in a heatexchange bath 122 (FIG. 10) that is held in a bath chamber 124 (FIG. 7).In one preferred embodiment, the fluid in the bath 122 is ethyleneglycol liquid. Alternatively, the fluid could be an ice bath, liquidnitrogen, or some other appropriate cold substance.

At least one TEC assembly 126 cools the bath 122. More preferably, thebath 122 is disposed between two TEC assemblies 126, 128, such that thebath 122 is cooled by the assemblies 126, 128. As was the case with thesystem 10, the system 100 preferably uses two cooling stages.Accordingly, a coolant inlet line 130 interconnects the heat exchangeelement 102 with the coolant return line 14 (FIG. 1), and the outlet 106of the heat exchange element 102 is connected to or made integrally withan inlet 132 of a second heat exchange element 134 that is in allessential respects identical to the first heat exchange element 102.After passing through the second exchange element 134, the coolant flowsthrough an outlet line 136 to the coolant supply line 16 (FIG. 1).Preferably, a thermal barrier 138 is disposed between the two coolingstages as shown, and an agitator 140 is disposed in the bath 122 to movethe fluid therein. The agitator 140 can be a rotating magnet or rotatingvane or other suitable agitator.

FIG. 11 shows the logic by which the controller 22 can control the speedof the pump 20 and/or the electrical current to the present TECs tothereby establish a desired patient temperature. At block 142, thecontroller receives the desired patient temperature T₀ from the inputdevice 26 or from preprogrammed logic. Also, the controller 22 receivesthe patient temperature signal T_(P) from the temperature sensor 28.Moreover, in the preferred embodiment the controller 22 receives thetime derivative dT_(p) /dt of the temperature signal T_(P) and the timeintegral Tdt of the temperature signal T_(p).

Moving to block 144, the controller determines a control signal bymultiplying the difference between the patient temperature signal T_(P)and the desired patient temperature T₀ by a biofunction f_(bio), andthen subtracting from this term the product of a derivative biofunctionf'_(bio) and the time derivative dT_(p) /dt of the temperature signalT_(P). Likewise, the time integral of temperature can be included as aterm. The biofunctions f_(bio) and f'_(bio) are empirically determinedand can be constants. With the above expression for the control signalin mind, it will be appreciated that the magnitude of the signal will belarge and its sign positive when patient temperature is high and rising.In contrast, the magnitude of the signal will be relatively small whenpatient temperature approaches the desired temperature and/or when thetime rate of change of patient temperature is large and negative, tothereby ameliorate the risk of overshoot. Accordingly, when the controlsignal is positive, additional cooling is indicated, with the magnitudeof the control signal being proportional to how much heat per unit timeis removed from the coolant by appropriately controlling coolant flowrate (by means of controlling the speed of the pump 20) and/or byappropriately controlling coolant thermal flux (by means of controllingthe TECs). The control step is indicated at block 146 in FIG. 11. In thecase wherein the control signal is negative (indicated that patienttemperature is below desired temperature and/or that the time gradientof coolant temperature is too negative), cooling can be stopped and,when provided, heating commenced by opening the heater inlet and outletvalves H_(in), H_(out), shutting the coolant inlet and outlet valvesC_(in), C_(out), and energizing the heater "H".

While the particular COOLING SYSTEM FOR THERAPEUTIC CATHETER as hereinshown and described in detail is fully capable of attaining theabove-described objects of the invention, it is to be understood that itis the presently preferred embodiment of the present invention and isthus representative of the subject matter which is broadly contemplatedby the present invention, that the scope of the present invention fullyencompasses other embodiments which may become obvious to those skilledin the art, and that the scope of the present invention is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean "one andonly one" unless explicitly so stated, but rather "one or more". Allstructural and functional equivalents to the elements of theabove-described preferred embodiment that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the presentclaims. Moreover, it is not necessary for a device or method to addresseach and every problem sought to be solved by the present invention, forit to be encompassed by the present claims. Furthermore, no element,component, or method step in the present disclosure is intended to bededicated to the public regardless of whether the element, component, ormethod step is explicitly recited in the claims. No claim element hereinis to be construed under the provisions of 35 U.S.C. §112, sixthparagraph, unless the element is expressly recited using the phrase"means for".

What is claimed is:
 1. A heat exchange system for a catheter,comprising:at least one heat exchange element connectable to thecatheter for receiving coolant from the catheter; and at least onethermal electric cooler (TEC) in thermal contact with the heat exchangeelement for heating or cooling the element such that coolant is returnedto catheter to heat or cool the catheter, wherein the heat exchangeelement includes plural hollow fibers.
 2. The system of claim 1, furthercomprising an interface sandwiched between the heat exchange element andthe TEC to removably couple the element to the TEC.
 3. The system ofclaim 1, further comprising at least one thermal interface between theheat exchange element and the TEC cooler.
 4. The system of claim 1, incombination with the catheter.
 5. The system of claim 1, furthercomprising a heater connectable to the catheter to heat coolant.
 6. Aheat exchange system for a catheter, comprising:at least one heatexchange element connectable to the catheter for receiving coolant fromthe catheter; and at least one thermal electric cooler (TEC) in thermalcontact with the heat exchange element for heating or cooling theelement such that coolant is returned to catheter to heat or cool thecatheter, wherein the heat exchange element includes a bag having pluralfluid paths through the bag.
 7. A heat exchange system for a catheter,comprising:at least one heat exchange element connectable to thecatheter for receiving coolant from the catheter; at least one thermalelectric cooler (TEC) in thermal contact with the heat exchange elementfor heating or cooling the element such that coolant is returned tocatheter to heat or cool the catheter; and at least first and secondheat exchange elements in series and first and second TEC assemblies,each heat exchange element being associated with a respective TECassembly.
 8. The system of claim 7, further comprising at least onethermal barrier between the elements.
 9. A cooling system for atherapeutic medical device, comprising:at least one heat exchanger madeat least partially of plastic, the heat exchanger receiving coolant fromthe medical device and returning coolant thereto; and a thermal electriccooler (TEC) in thermal contact with the heat exchanger for removingheat from the heat exchanger, wherein the heat exchanger includes pluralhollow fibers.
 10. A cooling system for a therapeutic medical device,comprising:at least one heat exchanger made at least partially ofplastic, the heat exchanger receiving coolant from the medical deviceand returning coolant thereto; and a thermal electric cooler (TEC) inthermal contact with the heat exchanger for removing heat from the heatexchanger, wherein the heat exchanger includes a bag having plural fluidpaths through the bag.
 11. The system of claim 10, further comprising aninterface sandwiched between the heat exchanger and the TEC to removablycouple the element to the TEC.
 12. The system of claim 10, furthercomprising at least one thermal interface between the heat exchanger andthe TEC cooler.
 13. The system of claim 10, wherein the device is acatheter, and the system is in combination with the catheter.
 14. Thesystem of claim 10, further comprising a heater connectable to thetherapeutic medical device to heat coolant.
 15. A cooling system for atherapeutic medical device, comprising:at least one heat exchanger madeat least partially of plastic, the heat exchanger receiving coolant fromthe medical device and returning coolant thereto; a thermal electriccooler (TEC) in thermal contact with the heat exchanger for removingheat from the heat exchanger; and at least first and second heatexchangers in series.
 16. The system of claim 15, further comprisingfirst and second TEC assemblies, wherein each heat exchanger isassociated with a respective TEC assembly.
 17. The system of claim 15,further comprising at least one thermal barrier between the elements.18. The system of claim 1, further comprising pump means communicatingwith the coolant for moving the coolant.
 19. A cooling system,comprising:catheter means for conveying coolant into a patient's bodywithout directly contacting the coolant with the body; heat exchangermeans communicating with the catheter means for receiving therefrom andreturning thereto coolant; cooling means in thermal contact with theheat exchanger means for conveying heat away from the heat exchangermeans; and at least first and second heat exchanger means in fluidseries with each other and first and second cooling means associatedwith the first and second heat exchanger means.